On Mon, 11 Mar 2024 at 11:34, Luis Henriques <lhenriques@xxxxxxx> wrote: > > Miklos Szeredi <miklos@xxxxxxxxxx> writes: > > > On Thu, 7 Mar 2024 at 19:17, Luis Henriques <lhenriques@xxxxxxx> wrote: > >> > >> This patch fixes the usage of mount parameters that are defined as strings > >> but which can be empty. Currently, only 'lowerdir' parameter is in this > >> situation for overlayfs. But since userspace can pass it in as 'flag' > >> type (when it doesn't have a value), the parsing will fail because a > >> 'string' type is assumed. > > > > I don't really get why allowing a flag value instead of an empty > > string value is fixing anything. > > > > It just makes the API more liberal, but for what gain? > > The point is that userspace may be passing this parameter as a flag and > not as a string. I came across this issue with ext4, by doing something > as simple as: > > mount -t ext4 -o usrjquota= /dev/sda1 /mnt/ > > (actually, the trigger was fstest ext4/053) > > The above mount should succeed. But it fails because 'usrjquota' is set > to a 'flag' type, not 'string'. The above looks like a misparsing, since the equals sign clearly indicates that this is not a flag. > Note that I couldn't find a way to reproduce the same issue in overlayfs > with this 'lowerdir' parameter. But looking at the code the issue is > similar. In overlayfs the empty lowerdir parameter has a special meaning when lowerdirs are appended instead of parsed in one go. As such it won't be used from /etc/fstab for example, as that would just result in a failed mount. I don't see a reason to allow it as a flag for overlayfs, since that just add ambiguity to the API. Thanks, Miklos
